Q&A with Kit Foster: March 15, 2012

Q. The 6- and 12-volt starting discussions in the Jan. 19 “Q&A” column did not mention one of the systems that Antique Auto Battery has been selling for years. I had one installed in a 1949 Lincoln with a freshly rebuilt 337-cid. flathead engine. A new 6- or 8-volt battery would hardly roll it over when cold and would not budge it when warm. The Antique Auto Battery 6/12 system worked like a charm as the engine rolled over very fast and started almost instantly. Its system consists of two 6-volt batteries in one case, a solenoid and all the needed cables and wires and comes with detailed, easy-to-follow installation instructions. You can call tech people at Antique Auto Battery with questions. I remember that I thought the price was very reasonable and that they have systems that can be applied to any 6-volt vehicle with a negative or positive ground. The Antique Auto Battery website has information on the 6/12 volt starting system at www.antiqueautobattery.com/accessories.html.

Bill Harper, Linwood, Mich.

A. Thanks for that information on another alternative. However, in the past week, I’ve also heard from another reader who agrees with my contention that most problems with 6-volt starting can be remedied by careful “grooming” of the electrical system. See below.

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Q. I would like to weigh in with a little experience from the trenches. Having worked on just about every type of 6-volt vehicle during the past 30 years, I find that most of the “quick fixes” offered (i.e., the 8-volt batteries, the 6/12 battery switches and the like) are ways to treat the symptoms, not fixing the actual problem. When all of the 6-volt vehicles were new, they started OK. Maybe they weren’t great by today’s standards, but well enough that people didn’t continually have dead batteries and towing companies were not overwhelmed with business.

The secret to making a 6-volt vehicle start is to have a minimum of 6 volts available at the starter. You can measure the voltage at the battery posts with the engine off. A 6-volt system is designed to have a minimum of 6.5 volts in the battery. Any less and things won’t work as they should. Next, check the voltage available at the starter battery post while the starter is cranking. There should not be more than a half volt of difference between battery voltage and starter voltage. If there is, it’s a sign of bad cables or dirty, corroded connections.

A 6-volt system is less forgiving than 12 volts and what you might be able to get away with in a 12-volt system will stop a 6-volt system dead in its tracks.

Check the starter draw following the shop manual instructions to be sure the starter is not drawing too much current. Excessive starter draw can come from things such as worn bushings inside the starter, which can allow the armature to drag against the field coils (magnets) inside the case. Poor internal connections inside the starter or broken wires within the armature can also cause problems.

Today, most 6-volt batteries are rated for at least 650 cranking amps. A 6-volt starter, even with a warm engine, should not require more than about 200 amps to crank the engine. So if the engine cranks slowly or not at all, it’s clear that the 650 cranking amps stored in the battery are not getting to the starter. Start with the cables and their connections. Most 6-volt vehicles came with 4-gauge cables from the factory. One-gauge or “double-ought” cables work better, because they can deliver more current from the battery with less resistance. Next, run the ground cable from the battery to one of the starter mounting bolts, or to the engine as close to the starter as you can get. Be sure you have a clean metal-to-metal contact on both ends and use toothed star washers under the bolt heads for good connection. This will create a direct path from battery to starter, and should increase starting system efficiency by about 30 percent.

Eight-volt batteries were a common solution in the “old days.” At first things seem to work well, until the factory charge is gone from the battery. When the 6-volt electrical system must recharge the 8-volt battery, the trouble begins. If the charging system was having trouble keeping up the 6-volt battery, it is not likely it will keep up an 8-volt battery, even if you “adjust the regulator” to 9.5 volts. Just because you adjust the regulator does not mean the generator will be able to produce the extra current. If you happen to get lucky and get more than 9 volts from the generator, all your dash gauges and all of the bulbs and accessories will have a short life. If you have a factory 6-volt radio, better unplug it so the smoke does not all leak out. Eight-volt batteries typically cause more problems than they fix.

There is no reason a 6-volt vehicle cannot start as easy as a 12-volt vehicle if everything is working as it should, you have a good battery, good cables and connections and a good working starter.

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